The structures of viruses and membranes will be studied using x-ray diffraction and electron microscopy to produce images of their structural organization and to characterize the structural changes which these assemblies undergo. It is necessary to visualize the details of the structures of these subcellular assemblies in order to understand how they function in the cell; to learn what controls their assembly, stability and dissolution; and to determine how they interact with other cell components during cell growth or infection, cell differentiation or transformation. The biological systems to be studied include several strains of filamentous bacteriophage, gap junctions, and bacteriophage phi 6. Relatively high resolution studies on the filamentous phages will result in detailed images of the protein-nucleic acid and protein-protein interactions that must govern the membrane associated assembly process. Structural studies on gap junctions in different conformational states will provide information about the nature and control of intercellular communication through these structures. Bacteriophage phi 6 is a complex, enveloped virus containing double-stranded RNA. It is more similar in structural organization and complexity to larger animal viruses such as Herpes or the RNA tumor viruses than any other bacteriophage. Once the technical difficulties intrinsic to the study of such a complex structure are overcome, similar studies on larger animal viruses will be initiated. Efforts will be concentrated on developing and using new methods for the structural analysis of macromolecular assemblies that will not crystallize. The fundamental problem in determining the structures of these assemblies is that diffraction data from non-crystalline specimens does not, in general, contain enough information to determine the structure. Our approach is to extract as much information as possible from the diffraction data and to use this information in coordination with electron microscope and other physical and chemical data in the structural analysis.